The addition of 11 new cases of the deadly Middle East Respiratory Syndrome (MERS), including a first in the Muslim holy city of Mecca, is starting to alarm officials at the World Health Organization (WHO).

"We are concerned about these new cases in health facilities in Saudi Arabia and in the UAE," Tarik Jasarevic, a WHO spokesman, told Bloomberg. "We are unaware at this point of the specific types of exposure in the health care facilities that have resulted in transmission of these infections."

A statement from the Saudi Arabia's health ministry said six of the new 11 MERS cases were in Jeddah, four in the Riyadh capital, and one in Mecca, bringing the total number of cases in the country to 272.

A report meantime by CBS News said a man in Athens, Greece has been confirmed and diagnosed with the MERS coronavirus, according to local health officials and WHO. The patient, aged 69 years old, just came from Jeddah. This is the first known case of MERS in Greece.

"We believe MERS is a zoonotic virus, meaning that the virus comes from animals, namely camels, and is transmitted to humans," Maria Van Kerkhove, a senior research fellow at Imperial College in London and a technical expert for the WHO, told Bloomberg. "The virus can also be transmitted from human to human, which we have seen between family members and health-care workers caring for MERS patients."

Last week, a Malaysian man who visited Saudi Arabia died from the virus.

Statistics wise, the number of MERS infections worldwide is relatively small. However, the WHO has started to take a closer look on the virus since reports of it extending beyond the Middle East started to get publicized. WHO has also taken particular note on the more than 40 per cent death rate among confirmed cases.